World in Transition: Climate Change as a Security Risk - WBGU

Erosion by wind and water is already a major problem,
and one that will be aggravated by rising temperatures
and a resulting increase in aridity. Where
land use has eliminated the dense vegetation cover,
thus exposing the soil directly to the effects of the
weather, e.g. following forest clearing or overgrazing,
desiccation facilitates rapid erosion of the surface
layer of soil. With loss of the fertile topsoil, including
as a result of landslides that occur due to lack
of vegetation cover, nutrients vital for plant growth
are lost, and this in turn leads to reduced agricultural
productivity. Often, this process of erosion also
entails compaction and encrustation of the soil surface.
This further reduces the water-carrying capacity
of the soil and accelerates soil degradation even
more (Schlesinger et al., 1990; Oldeman et al., 1991;
Oldeman, 1992). For this reason, erosion is given
particular attention as a factor when considering climate
change. Wind erosion is already a typical phenomenon
in semi-arid and arid zones. It occurs on
the fringes of most deserts, where the sparse plant
cover is highly sensitive to overgrazing and arable
soils are particularly prone to desiccation (e.g. the
Sahel region). But the west coast of South America,
the Mediterranean region, the Middle East, India
and north-eastern China are also affected by wind
erosion (USDA, 1998). It can therefore be assumed
that susceptibility to soil degradation due to erosion
will increase further in future in tandem with higher
air temperatures worldwide.
Alongside these physical factors, chemical degradation
of soils due to inappropriate agricultural practices
also causes loss of organic matter and nutrients,
especially in soils where fertility is poor, which in
turn is exacerbated by climatic changes. Inappropriate
intensive farming often results in soil impoverishment
and thereby to a decline in crop yields. A particularly
critical problem is posed by soil salinization,
which occurs only very rarely in nature. In agriculture,
soil salinization occurs primarily as a result of
artificial irrigation in semi-arid and arid zones, where
the evaporation rate is very high. These are the very
regions where even higher or extreme temperatures
are to be expected in future, along with highly variable
and generally scant annual precipitation. This category
includes for example North Africa, the Arabian
Peninsula, Central Asia, northern India and parts of
Pakistan. In China, Australia and Argentina, Mexico
and the west coast of South America, there are also
large areas with salinized soils (Oldeman et al., 1991;
Oldeman, 1992), and the trend is increasing. In the
medium term, the decline in yield can be reined in
for a time by switching to more salt-tolerant crops
(e.g. maize, wheat), but the scope of agriculture is
tightly constrained by plant metabolism. In the long
term, however, salinized soils will be irreversibly lost
Climate impacts upon human well-being and society 5.2
to agriculture and therefore also to food production.
This development is particularly relevant in terms of
world food supply; even today around 40 per cent of
the world’s food is produced on irrigated land. With
changing climatic conditions, the massive expansion
of irrigation agriculture predicted by many observers
will entail serious risks.
Soil salinization can also, however, occur in coastal
regions and regions with saline aquifers if there is
intrusion of seawater or fossil brine into the groundwater.
The reason for this, likewise, is inappropriate
and excessive use of water (Oldeman et al. 1991).
Whether and how the expected decline in food
production due to climate change might bring about
food crises and conflicts is discussed in the conflict
constellation ‘Climate-induced decline in food production’
(Section 6.3).
5.2.3
Climate change impacts upon storm and flood
events
Even today, storms and floods are responsible for
nearly 60 per cent of all natural disasters. Between
2000 and 2006, a total of 1,885 storm and flood disasters
were recorded around the globe, causing the
deaths of more than 57,000 people. Just under one
thousand million people were directly affected by
these disasters, and the economic damage totalled
nearly US$390 thousand million (CRED, 2006).
In many regions, climate change will increase the
risk of floods and storm damage. Reasons for this
include the anticipated increase in intense precipitation
events (Section 5.1.2) and in higher-intensity
tropical cyclones (Section 5.1.3), and sea-level rise
(Section 5.1.4).
These changes attributable to climate change are
further exacerbated by a number of other factors.
For example, deforestation in the upper reaches of
rivers leads to a reduction in water storage capacity
and thereby to increased surface run-off. In the
event of intense precipitation, this can lead to floods
(MA, 2005a). The severity of the risk posed to coastal
towns by sea-level rise and increasing tropical storm
intensity grows in direct proportion to rising population
density and concentration of assets and critical
infrastructure in many coastal regions. At the present
time, between 600 and 1,200 thousand million people,
in other words 10–23 per cent of the world’s population,
live in the vicinity of the coast, i.e. within 100km
of the coast and less than 100m above sea level. In the
future, the number of people living in coastal areas is
expected to rise even further (IPCC, 2007b). Moreover,
the subsidence of coastal cities that has been
observed as a result of groundwater abstraction and
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